1. Field of Invention
The invention relates to a wheel state adjustment system and a wheel state adjustment method for adjusting a predetermined quantity of state of a wheel, which may be, for example, an internal air pressure of a tire.
2. Description of Related Art
As noted in Japanese Patent Application Publication No. JP-A-7-137515 and No. JP-A-2003-94917, it is desirable to monitor various quantities of state of a wheel, such as an internal air pressure of a tire, in order to maintain the wheel in an appropriate state and achieve comfortable running of a vehicle. Accordingly, various related methods have been proposed for monitoring wheel quantities of state, like changes in the internal air pressure within the tire.
Many of the disclosed systems for monitoring wheel quantities of state and maintaining them appropriately, detect a wheel quantity of state such as the internal air pressure of the tire by using (a) sensors attached to a vehicle body, or (b) sensors provided in integrated units with vehicle instruments attached to the vehicle body.
However, recently, systems are being widely adopted that use sensors provided on each wheel to detect the respective wheel quantity of state such as the internal air pressure of the tire, and then transmit the detection results to an Electronic Control System (ECU), or the like, provided on the vehicle body. Such systems are epitomized by Tire Pressure Monitoring Systems (TPMS). In these systems, the sensors provided on each wheel are usually capable of switching between different operating modes depending on the wheel quantity of state. For example, some TPMS utilize sensors that switch between (a) infrequent detection of the wheel quantity of state at normal times, and (b) frequent detection of the wheel quantity of state when it is determined that an abnormality is likely to have occurred. By adopting such a configuration, it is possible to improve safety.
However, the sensors provided on the wheels often use a battery provided on each wheel as an energy supply rather than a battery provided on the vehicle body. Accordingly, in order to enable the sensors to be operated over extended periods using the respective wheel batteries, it is important to operate the sensors efficiently and reduce energy consumption. For example, some TPMS pro-actively adjust the tire internal air pressure to an appropriate level to suit the road being run along. With such systems, however, there is a possibility that use of this pro-active adjustment of the tire internal air pressure will cause the sensors to operate improperly and frequently detect the wheel quantity of state and transmit the detection results even when there is no likelihood that the wheel is in an abnormal state. However, as will be apparent, from the point of view of reducing energy consumption it is clearly undesirable if the sensors operate improperly and detect the wheel quantities of state more than necessary.